An example of a vial headspace inspection machine is described in U.S. Pat. No. 7,067,323, the disclosure of which is expressly incorporated by reference herein in its entirety. FIG. 9 shows a vial headspace inspection machine having a pre-inspection starwheel 22 which hands off cylindrically-shaped containers such as sealed generally optically transparent sample containers such as vials 14 to an inspection starwheel 28 for testing in an inspection region 18. Each of these starwheels 22, 28 includes pockets 23 to house vials 14, 30. Although sample vials 14 are handed off from pre-inspection starwheel 22 to inspection starwheel 28, a plurality of reference vials 30 (used a reference to continuously calibrate inspection sensors, to adapt for any changes in measurement conditions when analyzing the sample vials 14) are semi-permanently affixed to the inspection starwheel 28 (i.e., they are not handed off but rather continuously rotate with the inspection starwheel). As such, when feeding the pre-inspection starwheel 22 with sample vials 14, it is necessary to time such feeding so as to avoid introducing a sample vial 14 into the pocket 23 of pre-inspection starwheel 22, which otherwise would then cause the sample vial collide (or otherwise interfere) with a reference vial 30 already stored in a pocket 23 of the inspection starwheel 28.
Timing screw mechanisms are commonly used in vial headspace inspection machines to provide a way to control the position and speed when feeding vials 14 to coincide with pocket 23 locations of a pre-inspection starwheel 22 to facilitate loading of the starwheel pockets with the vials. FIGS. 1-3 show a related art timing screw mechanism 120 which includes a rotating timing screw 100. When used in vial headspace inspection machines, in order to prevent a sample vial 14 from colliding with a reference vial 30 already stored in a pocket 23 of the inspection starwheel 28, the screw 100 must pause its motion, e.g., for two vials every ½ turn of the pre-inspection starwheel 22 or equivalently every sixteen pockets.
In some vial headspace inspection machines, moving the starwheels 22, 28 as quickly as possible must be balanced by attempting to allow each vial 14, 30 to spend as much time being inspected in the inspection zone 18 to ensure the most accurate measurement possible. As such, vials 14 are fed and packed onto the inspection starwheel 30 as close as possible to each other. Accurate feed timing of the vials 14 thus becomes necessary in order to avoid unwanted collisions, jams and the like.
A drawback of the single timing screw 100 shown in FIGS. 1-3 is that it limits how closely vials 14 can be packed onto the starwheel 28. This is because if the vials 14 are too close to each other, when the screw tries to stop turning the last vial still remaining on the screw (i.e., the downstream-most vial) will interfere with the motion of the pre-inspection starwheel 22. To attempt to avoid this issue, the diameter of the screw 100 is increased at the very end of the screw in the form of a flare 102, thereby pushing the vial 14 into the pocket 23 of the pre-inspection starwheel 22, while leaving enough room so there is no interference with the stationary vial 14 behind it. Providing this flare 102 does not completely fix the issue and at the same time adds a complicated motion to the vials 14, which can lead to instability in the transport from the screw 100 to the pre-inspection starwheel 22.
Some known multiple screw systems include two separate screws positioned end to end with aligned axes of rotation. These screws are driven by motors at opposite ends of the system with a central support. This central support requires there to be a gap between the two screws, which can result in unstable handoff of containers at high speeds.